OF DENISON UNIVERSITY. 49 



GENUS POLYARTHRA, Ehr. 



A single species has so far been encountered and I am able, with 

 the works at hand, to discover no reason to doubt its identity with P. 

 platyptera of Ehrenberg. 



When swimming freely this animal seems to consist of two quad- 

 rilateral segments, the first, or head segment being considerable shorter 

 than wide in outline, while the body is a third longer than wide. The 

 trochal ciliation is slight. Two sensory organs are conspicuous upon 

 the front of the head and the eye occupies the middle of the first 

 segment near its posterior margin. The maxtax is very large and the 

 stomach is short, with a tubular intestine. There are two prominences 

 on either side of the body near the front, each bearing three lanceolate 

 spines. The egg is very large and is perhaps half as bulky as the 

 whole body. The contractile vessel is small and little could be seen 

 of the lateral vessels. The length is .10 mm. ; width, .08 mm,; setae, 

 .088 mm. long. This species seems rare and was found among plauts 

 in standing water during June and July of 1884 and 1885 near Min- 

 neapolis. 



The group of genera termed Macrodactylea or Longiseta includes 

 such animals as have a more or less elongate and frequently cylindrical 

 body, often strongly curved, and possess the following characters. 

 The cuticle is considerably indurated ; the terminal segment of the foot 

 is long ; there is usually a lack of symmetry exhibited by the claws or 

 maxtax; and the cilia are sparse upon the trochal disc. 



The following genera are at present included in the family : 

 Scaridium, Monura, Furcularia^ Diste?nma^ Monocerca^Mastigo- 

 cerca, Diurella, Heterognathus ^ Rattulus. 



GENUS DIURELLA, Bory de St. V. 



The body is more or less perfectly cylindrical, and curved either ventrally or 

 dorsally. The claws are rather long and frequently seem united, and are curved 

 ventrally, The eye is cervical and single. There is a sensory tube upon the 

 upper (dorsal) part of the disc. Three species are described, although doubt ex- 

 ists as to the specific value of one of these; they are D. tigris, Ehr., D. Rattulus^ 

 Eyferth, and D. stylata, Eyferth, to which a species is added below under the name 

 D. insignis. The common species in America is 



Diurella TIGRIS, {Ehr. ) Bory. 



The descriptions and figures of European authors vary remarkably 

 in this instance, but from them all we are able to gather sufficient tQ 



